U.S. Pat. No. 3,859,527 describes a method for recording and reproducing a high-energy radiation image using a panel for storing a radiation image comprising a stimulable phosphor which emits light when stimulated with visible or infrared radiations after exposure to such radiation (wherein high-energy radiation means an electromagnetic wave or corpuscular radiation such as X-rays, .alpha.-rays, .beta.-rays, gamma-rays, neutrons, ultraviolet rays, or the like).
U.S. Pat. No. 4,258,264 describes a method and apparatus for reproducing a radiation image by stimulating a storing phosphor with stimulating rays, the wavelengths of which are in the range from 600 to 700 nm, and detecting the stimulated light by means of a light detector, the detected light being in the range from 300 to 500 nm.
European patent application 111,893 describes a method for recording and reproducing a radiation image comprising the steps of (i) causing a radiation image storing panel to absorb a radiation passing through an object, such a panel containing a divalent europium activated barium fluorochloride phosphor, (ii) exposing said panel to an electromagnetic wave having a wavelength in the range from 400 to 550 nm to release the stored radiation energy as fluorescent light and (iii) detecting said fluorescent light.
U.S. Pat. No. 4,261,854 describes a barium fluorohalide phosphor represented by the formula BaFX:xCe,yA, wherein X is at least one halogen atom selected from the group consisting of chlorine, bromine and iodine, A is at least one metallic element selected from the group consisting of indium, thallium, gadolinium, samarium and zirconium, and x and y are numbers satisfying the conditions of 10.sup.-6 .ltoreq.x.ltoreq.0.2 and 10.sup.-5 .ltoreq.y.ltoreq.0.05, respectively.
European patent application 109,207 (corresponding to U.S. Pat. No. 4,654,533) describes a method for reading out a radiation image pattern recorded in a stimulable phosphor in which the phosphor is acnned by an Ar.sup.+ laser beam having a stimulating wavelength of about 514.5 nm.
GB patent 1,336,518 describes a phosphor material, prepared by activating a matrix consisting of lutetium and yttrium silicates with trivalent cerium, adapted for use with a fluorescent lamp and x-ray tube. When excited by electron beams or UV rays, this phosphor material emits a bluish-violet luminescence.
DE patent application 2,202,485 describes a cerium activated yttrium silicate phosphor suitable for flying-spot tubes, especially amplifying tubes for isotope dragnosis in gamma-chambers.
European patent application 88120638.7 describes terbium and/or cerium activated ternary lutetium-gadolinium-yttrium silicates for use in direct radiography When said phosphors are excited by x-rays, they emit violet, blue and green luminescence.
Generally speaking, the overall luminescence is a significant parameter for almost all phosphor applications. On the contrary, for radiographic applications using photostimulable phosphors, the relevant luminescence is that in the band of higher sensitivity of the photodetector which is coupled to the phosphor panel for detecting the emitted light Therefore, the general task in this field is to find more efficient phosphors.
U.S. Pat. No. 4,236,078 describes a method for recording and reproducing a radiation image by using visible or infrared radiation stimulable phosphors. In such patent, the inventor tested a series of stimulable phosphors and found that the SrS:Ce,Sm type phosphors (mentioned in the above cited U.S. Pat. No. 3,859,527) have a very low stimulability when they are stimulated both with visible and infrared radiation.
Some experiments, performed by the Applicant of the present patent application, have evidenced that, while LaOBr:Ce phosphor has a high stimulability, the addition of samarium as a second activator makes the stimulability of LaOBr:Ce,Sm phosphor be decreased to 30% of the value obtained in absence of samarium as a second activator.